1. Field of the Invention
The invention relates to a non-contact sensing system for monitoring the position and orientation of a rigid body in space. More specifically, the invention relates to such a system which can monitor the position and orientation of a pilot's helmet within the cockpit of a high performance tactical aircraft simulator.
2. Description of Prior Art
In order for aircraft simulators to provide a realistic simulation of aircraft flight, it is necessary to display a simulated surrounding environment to the simulator pilot. In currently available flight simulators, the displays are provided on the windscreens in the cockpit areas. These systems require one CRT for each such windscreen. With such a system, images of equal quality must be generated in each CRT regardless of where the pilot is looking. This is costly both in terms of hardware and computer time.
However, by projecting the image directly onto the visor of a pilot's helmet, a significant cost saving can be realized since the field of view is greatly reduced so that both the quality of the image (i.e. resolution) and the frame rate can be reduced. The field of view would be head slaved in order to provide an image which is instantaneously limited to the pilot's viewing area but which can be redirected to permit the pilot to "look" in any direction. It is also contemplated to track eye position or point of regard and provide a higher resolution image slaved to the eye's foveal area. In such a system, the pilot would perceive high resolution imagery wherever he looks. However, at any instant, the system is only required to produce high resolution images over a 15.degree. cone.
One of the difficulties associated with the use of helmet mounted visor displays is the maintenance of image stability. In order for the computer generated image to appear stationary as the pilot moves his head, the position of the pilot's helmet must be known relative to the simulator's fixed axis. This position is defined by three translation parameters (X, Y, Z) and three rotation parameters (Euler Angles). This information is also necessary in order to align the computer generated image with the frame of the windscreen. Thus, a (helmet) position sensing system is needed.
Currently available non-contact position sensing systems comprise a magnetic system as described in Raab, F. H., Blood, E. B., Steiner, T. O., and Jones, H. R., "Magnetic Position and Orientation Tracking System", IEEE Transactions on Aerospace and Electronic Systems, Vol. AES-15, No. 5, September 1979, pp. 709-718, and a V-slit system as described in Lewis, C. J. G., "Helmet Mounted Display and Sight Development", Proceedings of the American Helicopter Society, May 1979, pp. 79.17.1-79.17.13. However, both of these systems fail to meet required specifications.